Re: New speedo pitot/pickup... what should I use to seal it?
I would NOT use the rtv.
Even though it looks like it would seal good enough, it just doesn't stick good enough for the long term.
You may see this clear silicone stuff around shower doors or wherever. It looks water-tight, but if you dig your thumbnail under an edge, you can just peel it off.
With 4200 or 5200, you can't. This stuff is tenacious.
Use 4200 for things that you think you 'might' want to remove in the future.
Use 5200 for things that you never plan to remove.
Home Depot or Lowes has one or the other in smaller, 3 or 4oz tubes for under $8. Look in the paint dept, in the glue area.
This is important. Don't try to save a few bucks sealing holes in your transom.